IMPROVED, MINIMUM-INDUCTANCE, ELLIPTIC-CYLINDER Z-GRADIENT COIL USINGAXIAL AND AZIMUTHAL CURRENT FLOW

A new design for a minimum inductance, distributed current, longitudin al (z) gradient coil, fabricated on the surface of an elliptic cylinde r is proposed. By incorporating a small axial current, in addition to the purely azimuthal current which has been considered hitherto, this design greatly reduces the nonuniformity of the longitudinal magnetic field in transverse planes, which is associated with a purely azimutha l current flowing on the surface of an elliptic cylinder. For a coil w ith an axial ratio of the ellipse of 0.75, the deviation from gradient linearity along the z axis is <0.1% out to 0.66a where a is the lengt h of the semi-major axis. The nonuniformity of the field in the transv erse directions is <0.1% out to 0.5a, over most of the target-field re gion \z\ < 0.4a. (C) 1996 Academic Press, Inc.